Method for fabricating a high specific surface area mesoporous alumina

ABSTRACT

A method for fabricating a high specific surface area mesoporous alumina is disclosed, which includes the following steps: (a) providing a water solution containing an aluminum salt and a fluoro-surfactant; (b) adding concentrated hydrochloric acid to adjust the PH value of the solution to about 6.0 to 8.0; (c) aging the solution at 70° C. to 110° C. for 12 to 20 hours; (d) washing the precipitate with water; (e) washing the precipitate with an organic solvent; (f) drying the precipitate; and (g) sintering the precipitate in a furnace of 500° C. to 1000° C.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for fabricating an alumina,and more particularly, a method for fabricating a high specific surfacearea mesoporous alumina.

2. Description of the Related Art

According to pore sizes, porous materials are generally classified intomicroporous materials with a pore size less than 2 nm, mesoporousmaterials with a pore size between 2 nm and 50 nm, and macroporousmaterials with a pore size more than 50 nm. However, because the porediameters of microporous materials are too small and the pores ofmacroporous materials are not uniformly distributed, mesoporousmaterials without the above defects are widely used as catalysts,carriers for catalysts, gas adsorptive agents, filter materials, etc.Among the mesoporous materials, mesoporous alumina is easy to obtain andquite cheap so that it is used a great deal. Besides, with the greaterneeds for specialty chemicals, mesoporous alumina has a quite highprofit as a high unit priced fine-purification, adsorptive material.

The conventional method for manufacturing a mesoporous alumina is mainlydivided by starting material into a more expensive group of aluminumalkoxide and a cheaper group of aluminum salts such as aluminum nitrateand aluminum sulfate. Taking aluminum alkoxide as anstarting material,the method for fabricating a mesoporous alumina can produce a porousalumina with its porous diameter maintained on 11 nm. However, the costof aluminum alkoxide is high, and its specific surface area would beless than 150 m²/g when sintering at 1030° C. with the result that itwould be limited in practice.

Taking cheaper the aluminum salts, such as aluminum nitrate, aluminumsulfate, aluminum chloride and sodium aluminate, as thestartingmaterial, the cost could be lowered, but the mesoporous alumina obtainedby the conventional method has many defects in its porouscharacteristics. For example, the distribution of the pores is too wideto apply to a fine-purification system that requires high operatingdemands; the temperature for sintering is too low to use in petroleumcracking; the pore volume is too small, etc. Although the conventionalmethod could overcome the above limitations by adding a PEO surfactantas a structure directing material, the pore volume of its mesoporousproduct is still too small.

SUMMARY OF THE INVENTION

The present invention provides a fluoro-surfactant of formula (I),H(CF₂)_(m)COO(CH₂)_(n)COO(CF₂)_(m)H  formula (I)Wherein m and n are integers between 1 and 10.

The present invention also provides a method for manufacturing afluoro-surfactant of formula (I), which includes the following steps:(A) providing a dicarboxylic acid of the following formula (II) and afluoroalcohol of the following formula (III); (B) dissolving thedicarboxylic acid, the fluoroalcohol, and a p-toluenesulfonic acid in anorganic solvent to form a solution, wherein the molar number of thefluoroalcohol is over twice the molar number of the dicarboxylic acidand the p-toluenesulfonic acid acts as a catalyst; (C) refluxing andheating the solution to proceed the reaction; and (D) removing thesolvent from the solution by evaporation to obtain the product; whereinm and n are integers between 1 and 10.HOOC(CH₂)_(n)COOH  formula (II)H(CF₂)_(m)OH  formula (III)

Furthermore, the present invention provides a method for manufacturing ahigh specific surface area alumina, which includes the following steps:(A) providing a fluoro-surfactant of formula (I) or that of thefollowing formula (IV); (B) dissolving an aluminum salt and thefluoro-surfactant in water to form a solution, wherein the molar ratiobetween the fluoro-surfactant and the aluminum salt is 0.002-0.2:1; (C)adjusting the PH value of the solution to 6.0-8.0, by which aprecipitate is produced in the solution; (D) heating the solution at thetemperature of 80° C.-100° C. to proceed the aging; (E) washing theprecipitate with water; (F) washing the precipitate with an organicsolvent that can be miscible with water in order to replace the watercontent of the precipitate; (G) drying the precipitate; and (H)sintering the precipitate at the temperature of 400° C.-1100° C.H(CH₂)_(n)COO(CF₂)_(m)H  formula (IV)Wherein m and n are integers between 1 and 10. In this way, the methodof the present invention could reduce the use of the structure directingmaterials and also lower the cost. Besides, the method of the presentinvention could produce a mesoporous alumina of high specific surfacearea and homogeneous distribution of pore size.

In the method for fabricating a fluoro-surfactant of the presentinvention, the dicarboxylic acid can be any conventional organicdicarboxylic acid.

Preferably, the dicarboxylic acid is malonic acid and acetic anhydrate.In the method for fabricating a fluoro-surfactant of the presentinvention, the fluoroalcohol can be any conventional fluoroalcohol.Preferably, the fluoroalcohol is 2,2,3,3-tetrafluoro-1-propanol or2,2,3,3,4,4,5,5-octafluoro-1-pentanol. In the method for fabricating afluoro-surfactant of the present invention, the step (C) is reacted byrefluxing and heating preferably for 6 to 9 hours to gain vaporizedliquid with theoretical weight of water up to 80-95%. The method forfabricating a fluoro-surfactant of the present invention can selectivelyfurther comprise step (D′) to extract the product with another organicsolvent, then removing the organic solvent through evaporation to purifythe product, and it is preferable to evaporate the organic solvent byreducing pressure in the step (D′).

In the method for fabricating a high specific surface area alumina ofthe present invention, the aluminum salt can be any conventionalaluminum salt. Preferably, the aluminum salt is aluminum nitrate,aluminum sulfate, aluminum chloride or sodium aluminate. In the methodfor fabricating a high specific surface area alumina of the presentinvention, the fluoro-surfactant can be any conventionalfluoro-surfactant. Preferably, the fluoro-surfactant isBis(2,2,3,3-tetrafluoropropanyl) Maleate (BTFM),Bis(2,2,3,3,4,4,5,5-octafluoropentyl) Maleate (BOFM) or2,2,3,3-tetrafluoropropanyl acetate (TFPA). In the method forfabricating a high specific surface area alumina of the presentinvention, the PH value of the solution can be adjusted by anyconventional method in step (C), and it is preferable to adjust the PHvalue by adding concentrated hydrochloric acid. In the method forfabricating a high specific surface area alumina of the presentinvention, any organic solvent miscible with water can be used in step(F), and preferably, a solution with low boiling point and low surfacetension is used. In the method for fabricating a high specific surfacearea alumina of the present invention, any drying method, such as dryingby heating in an oil-bathed pot or drying by a vacuum oven, can be usedin step (G). In the method for fabricating a high specific surface areaalumina of the present invention, the time for aging in step (D) isbetween 12 and 20 hours. In the method for fabricating a high specificsurface area alumina of the present invention, the time for sintering isbetween 4 and 8 hours.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1-1 Synthesisof fluoro-surfactant (BTFM)

30.2 grams of 2,2,3,3-tetrafluoro-1-propanol, 10 grams of malonic acidand 7.31 grams of p-toluenesulfonic acid are added into 250 ml oftoluene. The mixture is reacted under reflux for 8 hours and then thevaporized liquid with theoretical weight of water up to 90% is collectedby using a Dean-Stark trap. 15 grams of 2,2,3,3-tetrafluoro-1-propanolis added again and refluxed for 4 hours. The solvent is evaporated andthen extracted three times with ethyl acetate. The ethyl acetate isremoved by reduced pressure steam with the outer temperature of 115° C.and 0.2 torr to obtain 23.3 grams ofBis(2,2,3,3-tetrafluoropropanyl)Maleate (BTFM).

¹H NMR (300 MHz, CDCl₃; ppm): δ 3.56 (s, 2H), 4.54 (t, J=12.6 Hz, 4H),5.86 (tt, J=52.9 Hz, J=3.6 Hz, 2H)

¹³C NMR (75 MHz, CDCl₃, ppm): δ 39.9 (s), 60.3 (t, J=28.9 Hz), 109.2(tt, J=248.2 Hz, J=35.9 Hz), 113.9 (tt, J=248.3 Hz, J=27.8 Hz), 164.5(s).

EXAMPLE 1-2 Synthesis of fluoro-surfactant (BOFM)

45.0 grams of 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 10 grams of malonicacid and 7.31 grams of p-toluenesulfonic acid are added into 200 ml oftoluene. The mixture is reacted under reflux for 4 hours and then thevaporized liquid with theoretical weight of water up to 90% is collectedby using a Dean-Stark trap. The solvent is evaporated and then extractedthree times with ethyl acetate. The ethyl acetate is removed by reducedpressure steam with the outer temperature of 115° C. and 0.2 torr toobtain 45.1 grams of Bis(2,2,3,3,4,4,5,5-octafluoropentyl) Maleate(BOFM).

¹H NMR (400 MHz, CDCl₃ ppm: δ 3.58 (s, 2H), 4.64 (t, J=13.6 Hz, 4H),6.02 (tt, J=52.0 Hz, J=5.4 Hz, 2H)

¹³C NMR (75 MHz, CDCl₃, ppm): δ 40.0 (s), 60.3 (t, J=26.9 Hz), 107.8(tt, J=253.1 Hz, J=30.8 Hz), 110.2 (m), 114.4 (tt, J=256.4 Hz, J=30.5Hz), 164.2 (s).

EXAMPLE 1-3 Synthesis of fluoro-surfactant (TFPA)

26.4 grams of 2,2,3,3-tetrafluror-1-propanol, 30.6 grams of aceticanhydrate and 15.2 grams of toluol-4-sulfonic acid monohydrate arereacted at the outer temperature of 120° C. for 12 hours and then arecooled down to room temperature. The product is washed with 100 ml ofethyl ether and 50 ml of pure water for three times. The ethyl etherlayer is then distilled. The outer temperature is set at up to 90° C.When there is no distillation any more, the product is washed with 100ml of pure water for three times to obtain 14.67 grams of2,2,3,3-tetrafluoropropanyl acetate (TFPA).

¹H NMR (300 MHz, CDCl₃, PPM): δ 2.06 (s, 3H), 4.39 (t, J=13.2 Hz, 2H),5.83 (tt, J=53.6 Hz, J=3.4 Hz, 1H).

The lipohydrophilic part of the fluoro-surfactant of the presentinvention is a carbon-fluorine chain that has a better hydrophobicitythan general carbonhydrogen chain.

In the method for manufacturing a mesoporous alumina of the presentinvention, a surfactant of fluoro dicarboxylic acid or fluoro carboxylicacid can be used as the structure directing material. In thisembodiment, the fluoro dicarboxylic acid such as BTFM and BOFM and thefluoro carboxylic acid such as TFPA are used respectively as thestructure directing material to prepare the mesoporous alumina.

EXAMPLE 2-1 Preparation of Mesoporous Alumina with BTFM Surfactant

10 grams of sodium aluminate is added into 100 ml of water and stirredto dissolve. 0.1 gram of BTFM surfactant is added and stirred to mixwith the solution. Concentrated hydrochloric acid is dripped into thesolution until its PH value is 7. Stirring is then stopped and thebeaker is moved into an oil-bathed pot to age at the outer temperatureof 90° C. for 16 hours. The product is washed and stirred with 300 ml ofpure water and then isolated centrifugally for three times. Followingthe above step, the product is then washed with 300 ml of methanol forthree times. The resulting product is put into the oil-bathed pot anddried at 90° C. for 2 hours. The product is moved into a vacuum oven anddried at 90° C. for 16 hours. The dried product is ground and then movedinto a furnace to sinter at 1000° C. for 5 hours to obtain a mesoporousalumina the porous volume of which is 0.76 cm³/g, the pore diameter ofwhich is 17.8 nm and the specific surface area of which is 168 m²/g.

EXAMPLE 2-2 Preparation of Mesoporous Alumina with BOFM Surfactant

10 grams of sodium aluminate are added into 100 ml of water and arestirred to dissolve. 0.5 gram of BOFM surfactant is added and stirred tomix with the solution. Concentrated hydrochloric acid is dripped intothe solution until its PH value is 7. Stirring is stopped and the beakeris moved into an oil-bathed pot to age at the outer temperature of 90°C. for 16 hours. The product is washed and stirred with 300 ml of purewater and then isolated centrifugally for three times. By the same way,the product is washed with 300 ml of methanol for three times. Theresulting product is put into the oil-bathed pot and dried at 90° C. for2 hours. The product is moved into a vacuum oven and dried at 110° C.for 16 hours. The dried product is ground and then moved into a furnaceto sinter at 1000° C. for 5 hours to obtain a mesoporous alumina theporous volume of which is 0.66 cm³/g, the pore diameter of which is 13.7nm and the specific surface area of which is 192.2 m²/g.

EXAMPLE 2-3 Preparation of Mesoporous Alumina with TFPA Surfactant

10 grams of sodium aluminate is added into 100 ml of water and stirredto dissolve. 2.5 grams of TFPA surfactant is added and stirred to mixwith the solution. Concentrated hydrochloric acid is dripped into thesolution until its PH value is 7. Stirring is stopped and the beaker ismoved into an oil-bathed pot to age at the outer temperature of 90° C.for 16 hours. The product is washed and stirred with 300 ml of purewater and then isolated centrifugally for three times. By the same way,the product is washed with 300 ml of methanol for three times. Theresulting product is put into the oil-bathed pot and dried at 90° C. for2 hours. The product is moved into a vacuum oven and dried at 110° C.for 16 hours. The dried product is ground and then moved into a furnaceto sinter at 1000° C. for 5 hours to obtain a mesoporous alumina theporous volume of which is 1.05 cm³/g, the pore diameter of which is 15.8nm and the specific surface area of which is 257 m²/g.

EXAMPLE 2-4 Preparation of Mesoporous Alumina with BTFM Surfactant andby Sintering at 500° C.

10 grams of sodium aluminate is added into 100 ml of water and stirredto dissolve. 0.5 gram of BTFM surfactant is added and stirred to mixwith the solution. Concentrated hydrochloric acid is stirred into thesolution until its PH value is 7. Stirring is stopped and the beaker ismoved into an oil-bathed pot to age at the outer temperature of 90° C.for 16 hours. The product is washed and stirred with 300 ml of purewater and then isolated centrifugally for three times. By the same way,the product is washed with 300 ml of methanol for three times. Theresulting product is put into the oil-bathed pot and dried at 90° C. for2 hours. The product is moved into a vacuum oven and dried at 110° C.for 16 hours. The dried product is ground and then moved into a furnaceto sinter at 500° C. for 5 hours to obtain a mesoporous alumina theporous volume of which is 0.68 cm3/g, the pore diameter of which is 6.1nm and the specific surface area of which is 426 m²/g.

The method for fabricating a high specific surface area alumina of thepresent invention adopts a method of solvent replacement to remove thewater from the hydrated alumina by using a solvent miscible with water,such as methanol. This method can prevent a result in which the poreswould collapse to make the reduction of the porous volume while dryingthe precipitate due to its high hydrous capacity and when there are nostructure directing materials. Besides, in comparison with conventionalways to take PEO as structure directing material, thefluoride-surfactant used in the present invention the lipohydrophilicterm of which is a carbon chain containing fluorine has a betterhydrophobicity than a general carbon chain containing hydrogen.Therefore, it can efficiently form microcells to support the pores,reduce the amount of the structure directing materials, and diminish theresistance of draining and drying. The conventional technology obtains amesoporous alumina that has specific surface area of 166.5 m²/g andporous volume of 0.79 cm³/g with a surfactant of a molar ratio of 0.15and sintering at 900° C. However, the present embodiment only uses asurfactant of a molar ratio of 0.12 sintered at 1000° C. to gain amesoporous alumina of higher specific surface area. Further, the presentinvention can also obtain a mesoporous alumina with a specific surfacearea of 426 m²/g by using few surfactants of a molar ratio of 0.012sintered at 500° C. The resulted specific surface area is much higherthan that of the product made by conventional surfactant of molar rationof 0.4 sintered at the same temperature. In other words, the method forfabricating a high specific surface area alumina of the presentinvention improves a lot the use of a surfactant and the porouscharacteristics of the product.

In addition, measured by BET, the distribution of the pores is moreconcentrated than ever before, i.e., the porous diameter of themesoporous alumina prepared by the present embodiment ranges from 2 to20 nm.

COMPARATIVE EXAMPLE 1 Preparation of Mesoporous Alumina without AddingSurfactant

10 grams of sodium aluminate is added into 100 ml of water and stirredto dissolve. Concentrated hydrochloric acid is dripped into the solutionuntil its PH value is 7. Stirring is stopped and the beaker is movedinto an oil-bathed pot to age at the outer temperature of 90° C. for 16hours. The product is washed and stirred with 300 ml of pure water andthen isolated centrifugally for three times. By the same way, theproduct is washed with 300 ml of methanol for three times. The resultingproduct is put into the oil-bathed pot and dried at 90° C. for 2 hours.The product is moved into a vacuum oven and dried at 110° C. for 16hours. The dried product is ground and then moved into a furnace tosinter at 1000° C. for 5 hours to obtain a mesoporous alumina the porousvolume of which is 0.32 cm³/g, the pore diameter of which is 15.0 nm andthe specific surface area of which is 81.9 m²/g.

The steps of comparative example 1 are identical to those of theexamples, except that there is no fluoride-surfactant added. However,the specific surface area and the porous volume of the mesoporousalumina provided by comparative example 1 are much smaller than those ofthe examples. As a result, the fluoride-surfactant of the presentinvention does help to support the porous microcells.

COMPARATIVE EXAMPLE 2 Preparation of Mesoporous Alumina without WashingProcedure and Surfactant

10 grams of sodium aluminate is added into 100 ml of water and stirredto dissolve. Concentrated hydrochloric acid is dripped into the solutionuntil its PH value is 7. Stirring is stopped and the beaker is movedinto an oil-bathed pot to age at the outer temperature of 70° C. for 5.5hours. The product is moved into a vacuum oven and dried at 70° C. for15 hours. The dried product is ground and then moved into a furnace tosinter at 1000° C. for 5 hours to obtain a mesoporous alumina the porousvolume of which is 0.096 cm³/g, the pore diameter of which is 10.9 nmand the specific surface area of which is 35.1 m²/g.

Comparing the comparative example 2 with comparative example 1, nosurfactants are added and all manufacturing conditions are the same,except that the mesoporous alumina of comparative example 2 is preparedwithout the washing procedure. However, the porous volume, porousdiameters and the specific surface area of the comparative example 2 aresmaller than those of the comparative example 1. As a result, the methodfor replacing water with organic solvent miscible with water used in themanufacturing method of the present invention can prevent the pores fromcollapsing, and so prevent reduction of the porous volume due todryness.

Fine-Purification Test

Taking the mesoporous alumina obtained by the present invention andmesoporous alumina AC61 to proceed a liquid crystal adsorptivepurification. The present invention measures the original specificresistance of recycled liquid crystal. Then, the recycled liquid crystalis mixed with 5 wt % of adsorptive materials and the mixture is stirred.After filtering with 0.2 μm PTFE film, the specific resistance of theadsorptive purified liquid crystal is measure to obtain a liquid crystalspecific resistance, as shown in Table 1. In Table 1, it is obvious thatthe method for manufacturing mesoporous alumina of the present inventionhas better fine-filtering and adsorptive characteristics than that ofthe merchandise mesoporous alumina. TABLE 1 Adsorptive PurificationAdsorptive Material Original Resistance by 5 wt % AC61 3.6 × 10¹² Ωcm5.9 × 10¹² Ωcm Alumina of the present 1.8 × 10¹² Ωcm 2.9 × 10¹³ Ωcminvention

Although the present invention has been explained in relation to itspreferred embodiments, it is to be understood that many other possiblemodifications and variations can be made without departing from thescope of the invention as hereinafter claimed.

1. A fluoro-surfactant of the following formula (I):H(CF₂)_(m)COO(CH₂)_(n)COO(CF₂)_(m)H  formula (I) wherein m and n areintegers between 1 and
 10. 2. A method for fabricating afluoro-surfactant of the following formula (I), which contains steps of:H(CF₂)_(m)COO(CH₂)_(n)COO(CF₂)_(m)H  formula (I) (A) providing adicarboxylic acid of the following formula (II) and a fluoroalcohol ofthe following formula (III):HOOC(CH₂)_(n)COOH  formula (II)H(CF₂)_(m)OH  formula (III) (B) dissolving said dicarboxylic acid, saidfluoroalcohol, and a p-toluenesulfonic acid in an organic solvent toform a solution, wherein the molar number of said fluoroalcohol is overtwice the molar number of said dicarboxylic acid and saidp-toluenesulfonic acid acts as a catalyst; (C) refluxing and heatingsaid solution to proceed the reaction; and (D) removing the solvent fromsaid solution by evaporation to obtain the product; wherein m and n areintegers between 1 and
 10. 3. The method for fabricating afluoro-surfactant as claimed in claim 2, wherein said dicarboxylic acidis malonic acid or acetic anhydrate.
 4. The method for fabricating afluoro-surfactant as claimed in claim 2, wherein said fluoroalcohol is2,2,3,3-tetrafluoro-1-propanol or 2,2,3,3,4,4,5,5-octafluoro-1-pentanol.5. The method for fabricating a fluoro-surfactant as claimed in claim 2,wherein said step (C) is reacted by refluxing and heating for 6 to 9hours to gain vaporized liquid with theoretical weight of water up to80-95%.
 6. The method for fabricating a fluoro-surfactant as claimed inclaim 2 further comprising a step (D′) in which to extract the productwith another organic solvent and then removing said organic solventthrough evaporation to purify the product.
 7. The method for fabricatinga fluoro-surfactant as claimed in claim 6, wherein said organic solventis evaporated by reducing pressure in said step (D′).
 8. A method forfabricating a high specific surface area alumina, which includes thefollowing steps of: (A) providing a fluoro-surfactant of the followingformula (I) or that of the following formula (IV):H(CF₂)_(m)COO(CH₂)_(n)COO(CF₂)_(m)H  formula (I)H(CH₂)_(n)COO(CF₂)_(m)H  formula (IV) wherein m and n are integersbetween 1 and 10; (B) dissolving an aluminum salt and saidfluoro-surfactant in water to form a solution, wherein the molar ratioof said fluoro-surfactant to said aluminum salt is 0.002-0.2:1; (C)adjusting the PH value of said solution to 6.0-8.0, by which to producea precipitate in the solution; (D) heating said solution at thetemperature of 70° C.-110° C. to proceed aging; (E) washing saidprecipitate with water; (F) washing said precipitate with an organicsolvent that can be miscible with water in order to replace the watercontent in said precipitate; (G) drying said precipitate; and (H)sintering said precipitate at the temperature of 500° C.-1000° C.
 9. Themethod for fabricating a high specific surface area alumina as claimedin claim 8, wherein said aluminum salt is aluminum nitrate, aluminumsulfate, aluminum chloride or sodium aluminate.
 10. The method forfabricating a high specific surface area alumina as claimed in claim 8,wherein said fluoro-surfactant is BTFM, BOFM or TFPA.
 11. The method forfabricating a high specific surface area alumina as claimed in claim 8,wherein concentrated hydrochloric acid is added to adjust the PH valueof said solution.
 12. The method for fabricating a high specific surfacearea alumina as claimed in claim 8, wherein said organic solventmiscible with water used in said step (F) is a solution with low boilingpoint and low surface tension.
 13. The method for fabricating a highspecific surface area alumina as claimed in claim 8, wherein the methodto dry the precipitate used in said step (G) is by heating in anoil-bathed pot or by a vacuum oven.
 14. The method for fabricating ahigh specific surface area alumina as claimed in claim 8, wherein thetime for aging in said step (D) ranges from 12 to 20 hours.
 15. Themethod for fabricating a high specific surface area alumina as claimedin claim 8, wherein the time for sintering in said step (H) ranges from4 to 8 hours.